[Digikam-devel] Re: Logic error

[Marcel Wiesweg]

> Basically since we inherit from QWidget most of the time, a virtual
> destructor should always be used, since QWidget provides virtual methods?

Yes, any QObject-derived class will already have a virtual destructor.

The simple rule is "make your destructor virtual if your class has any virtual 
functions":
http://www.parashift.com/c++-faq-lite/virtual-functions.html#faq-20.7

As far as I see GCC always gives a warning if you have virtual methods and not 
virtual destructor in a base class

There is a small group of classes which will not need a virtual destructor: If 
a class has a private QSharedDataPointer d-pointer, then it will usually not 
be subclassed and not be created on the heap.
And fast "inline" classes, like DColor, shouldnt have this.

> Like I said I converted every destructor to be virtual in my branch and I
> can not see any slowdowns.

I would say there is the "slowdown" of the indirect call through the vtable, 
which should be negligible in most cases. For memory cost, I think every 
object will get an additional pointer.

The question is, which classes remain if you keep aside all QObject-derived 
ones, which have it already, and all implictly/explicily-shared classes, which 
dont need it?

Marcel